Vehicles may be fitted with evaporative emission control systems to reduce the release of fuel vapors to the atmosphere. For example, evaporative emissions control systems may include a carbon canister coupled to a fuel tank for adsorbing refueling, diurnal and running loss hydrocarbon vapors from the fuel tank during engine-off conditions. At a later time when the engine is in operation, a canister purge valve coupled within a purge line coupling the canister and the engine intake manifold is opened, which allows the vapors to be purged into the engine intake manifold for use as fuel.
Activated carbon inside the canister is used to adsorb the vaporized hydrocarbons. The carbon comprises of tiny pellets that have microscopic pores to trap the hydrocarbons. Over time, carbon dust breaks away from the pellets and migrate to the purge valve. Consequently, leaks may occur in the purge valve. Leaky purge valves are expensive to replace and may cause damages to the fuel tank.
In order to mitigate carbon dust migration from the canister to the purge valve, a canister filter may be employed within the canister near a purge port to trap the carbon dust and therefore prevent the carbon dust from clogging the purge valve. However, the canister filter may become restricted over a period of time. For example, activated carbon breakdown due to liquid fuel entering the canister may cause the canister to clog. When the canister filter is restricted, the engine vacuum may not be able to reach the canister, thereby resulting in failed purging operations. The inability to purge causes the canister to saturate, which leads to increased hydrocarbon breakthrough to the atmosphere, and hence increased evaporative emissions. Further, evaporative emissions leak diagnostics that use engine vacuum to evacuate fuel tank and perform bleed up analysis may be affected due to the clogged carbon filter preventing the engine vacuum from being applied to the tank. Still further, in hybrid vehicles, a highly restrictive canister filter may impede fuel tank depressurization prior to a refueling sequence.
The inventors herein have recognized the above issues, and have developed systems and methods to at least partially address them. In one example, a method, comprising: indicating restriction of an integrated filter of a carbon canister responsive to a duration for a pump disposed in a vent line between the canister and atmosphere to reduce a pressure of an evaporative emissions control system to a reference pressure being less than a first threshold duration. In this way, diagnostics may be performed to determine if the filter is clogged.
As an example, during engine-off conditions, an ELCM pump disposed in a vent line between the canister and atmosphere may be operated to evacuate a portion of the evaporative emissions control system with the purge valve and the FTIV closed (also referred to herein as canister side of the evaporative emissions control system). As such, a duration to reach a reference pressure is proportional to the volume in the system. Therefore, if the canister filter is fully restricted, a purge line between the purge valve and a purge port of the canister cannot be evacuated by the ELCM pump due to the clogged filter blocking accessibility to the purge line. Since the purge line between the purge port and the purge valve has considerable volume, when the canister filter is fully restricted, a volume of the emissions control system that is available for evacuation by the ELCM pump decreases. Consequently, the duration to evacuate the emissions control system is reduced. Therefore, restriction of a canister filter may be diagnosed based on a duration to evacuate the canister side of the evaporative emissions control system to a reference pressure being less than a threshold duration, where the threshold duration is based on a duration to evacuate a new canister filter.
If the canister is partially restricted, the entire volume of the canister side is accessible to the ELCM pump. However, the ELCM pump may take a longer duration to evacuate the canister side of the evaporative emissions control system as the restricted filter may decrease the evacuation rate. Therefore, if the canister is partially restricted, the duration to evacuate the canister side to the reference pressure is greater than a second threshold duration, where the second threshold duration is greater than the first threshold duration.
Further, when the canister side of the evaporative emissions control system is at the reference pressure, an initial pressure difference across the canister at a time when the purge valve is commanded open may further indicate if the canister is partially restricted or fully restricted. For example, if the canister filter is fully restricted, the initial pressure difference across the canister, as measured by a MAP sensor and an ELCM pressure sensor, may be greater than a threshold difference. If the canister filter is partially restricted, the initial pressure difference is less than the threshold. If partial restriction of the canister filter is confirmed, a vehicle controller may estimate a remaining life time of the canister filter by monitoring a rate of vacuum decay and a duration for the evaporative emissions control system to stabilize to the atmospheric pressure after opening the purge valve.
In this way, an existing ELCM pump that is utilized for evaporative emissions leak detection routines is also utilized to diagnose a canister filter. By diagnosing restriction of the canister filter and estimating a remaining lifetime of the canister filter, a vehicle operator may be altered of a failing canister filter condition and prompted to take corrective actions (such as replacing the canister filter or cleaning the canister filter) before the canister becomes fully restricted, thus saving on warranty and/or repair costs. Further, if canister filter restriction is diagnosed, evaporative emissions leak diagnostics may not be performed until corrective actions are taken, thereby reducing evaporative emissions leak diagnostics failure due to clogged canister filter. Still further, by diagnosing canister filter restriction, and taking necessary corrective actions based on the diagnosis, purging efficiency may be maintained at a desired level. Consequently, emissions may be reduced and fuel economy may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.